Cold Spark
by Deadfang1
Summary: She nearly killed her sister and almost destroyed her home. He killed his brother and executed his mentor. Perhaps together they will find redemption. And... just maybe... something more between each other. Two broken souls seek comfort from their traumatic pasts. [OptimusxElsa] Takes place after Dark of the Moon. AU so no KSI or Galvatron. Rating M for violence blood and language.
1. Chapter 1

**[A/N] Idea for a story that popped into my head. Let me know what you think and if you want more of this. No I'm not abandoning Titania's Idiot. Just wanted to take a break for a minute and try something else.**

 **CHAPTER 1 : Once More Into the Breach**

Location: Diego Garcia military installation

Pain. That's what Optimus Prime was feeling right now. Pain. Not the clang and clatter of tools in his audio receptors, not the warm concrete under his pedes, not the salty ocean breeze on his plates. Only the pain of his arm being reattached after his fight in Chicago. In an effort to drown out the sensation of wires being soldered back together and the flaring heat from the welds in his shoulder; he reflected on this most recent battle. Megatron, the one he once called brother that stood by his side in an effort to reorganize Cybertron's caste system into something better for all Cybertronians, was dead. Sentinel Prime, his mentor and former leader of the Autobots, he had executed himself for his betrayal. Shockwave, the infamous Decepticon scientist, he had torn apart with his bare servos. The Driller Beast that Shockwave had once commanded, he had blown apart with his flight pack. Soundwave, Starscream and Barracade were killed off by Bumblebee and the human's armed forces. The infamous assassins, the Decepticon Dreads; Crankcase, Crowbar and Hatchet, were slaughtered by Ironhide and Sideswipe. With their command structure destroyed the Decepticons, those that still functioned had no choice but to flee to the shadows. Truly a great victory for both their species and a hard won time of peace. The War of Cybertron; that began thousands of years in the past and millions of light years away, was finally over.

Yet this was a bittersweet victory that came at a high cost. Countless human lives were lost in the hours of the Autobot's first exile. The city of Chicago suffered catastrophic damage. But the Autobots did not come out unscathed either. Wheeljack an Autobot inventor was executed by Barracade when they were captured during the battle. Ironhide...known as the most ruthless 'con killer of the Autobot army; bodyguard, sworn protector and old friend of Optimus Prime, was dead. Betrayed by their former leader Sentinel, he was shot in the back and left to rust. Optimus felt no remorse when pressed the barrel of Megatron's scatter-gun to Sentinal's helm and pulled the trigger. Thankfully his thoughts of the war plaguing his processor were interrupted by the voice of an old friend.

"Alright you over-sized Sparkling... your done. Test it out for me." Ratchet, Optimus' Chief Medical Officer, droned out.

Bright blue optics flared to life as the Prime took in his surroundings; first his old friend then turned to his handiwork. With a simple thought from his processor, he brought up his arm flexing first the shoulder joint where the most damage was when Sentinel stabbed him then tore the limb clean off, then the elbow, then the wrist and finally his digits.

"Thank you old friend. You always come through for us." The Autobot leader rumbled Standing from his seated position on the berth in Ratchets lab he nodded his thanks and strode out the massive door to the runway outside followed closely by the old medic. Diego Garcia... a temporary home given to the Autbots until they can figure a way off this planet under the watchful eye of their good friend, Major William Lennox. The Xanthium, the ship that brought the second wave of Autobots, was destroyed by Starscream when they were first exiled by the world's governments. The Decepticon fleet was anihilated into oblivion when the space bridge collapsed. But Ratchet had a thought to use the remains of Sentinals Space Bridge Pillars to craft one of his own. With the control Pillar destroyed and Sentinel dead, the rest became unlocked from his control and went into a standby mode. Ratchet had made great strides in his contruction after retrieving only twenty or so pillars. The real trick was building a new control pillar for the whole system. Even with most of the world against them Optimus continued doing what he could to smooth relations between humans and Cybertronians, mostly however, it was meant to keep them off Ratchet's aft so he could focus on his work. Tomorrow would be the first test for the new pillars. The plan was quite simple: set up a stable bridge to the moon's surface, transport as much salvage, energon rations and parts they could find, then remotely destroy the pillars to ensure mankind cannot use it and finally begin repairs to the crash-landed Ark to leave the system in search of a new home.

"Optimus you should get some recharge. I think you've earned it." Ratchet once again broke him from his reverie. Optimus was ready to protest but Ratchet beat him to it. "Slag that... consider it a doctor's orders. Look... Megatron is dead and with the last shards of the Allspark destroyed and with the Matrix of Leadership in our servos, he can't return again. The Decepticons are gone... the war is over."

"Perhaps you are right. I do feel rather drained... I shall be in the next hanger over should anything happen." Ratchet nodded then turned back to his lab while Optimus shifted into his alt-form, a blue and red flame patterned Peter built semi truck, thankfully his arm was able to shift flawlessly. He rolled into the hanger and rested on his tires in a quiet corner, letting a hiss of air escape his vents akin to relieved sigh. That was the exact moment that it finally struck Optimus straight to his spark. ' _It's over... after everything that has happened all those years ago... It's all finally over. Now we must start over... yet I feel unsure if I should continue to lead them... What they need is somemech that's has the Know-how to start us off new. They don't need an old run-down mech who all they've known is war and death. Perhaps... Ratchet...'_ With that Optimus drifted off into recharge.

"Ratchet what's our status?" Optimus requested the next morning as he moved to the tarmac just outside the lab where Ratchet had set up the pillars in a large square pattern. Most of what was to be taken with them to the Ark was stacked nearby. He had ordered the rest of the Autobots to remain inside to ensure their safety.

"From what I can tell with my scans alone, It's fully operational." Ratchet said not even bothering to look up from the console his optics were seemingly glued to.

"Very well... Fire it up then."

Ratchet then activated the newly constructed control pillar. With a pulsing hum the bridge activated with a crackling of lightning that soon evened out with the pulse.

"We're good Optimus. It's looking-" Ratchet never got to finish as the bridge suddenly destabilized without warning. The once calm bridge became a singularity pulling anything it could inside. Ratchet was lucky enough to grab onto the door of the lab nearly ripping it off. Looking over his shoulder he caught a glimpse of his old friend and fearless leader as he was pulled ever closer. The only thing holding him back was the sword he had driven into the ground.

 **"Ratchet! Take care of them... It's up to you now!"** Optimus boomed from his kneeling position.

Then his blade slipped and he fell back into the swirling vortex. On contact a blinding light forced Ratchet to shutter his optics until it passed. When it did he no longer felt the force of the singularity. He stood to see it had disappeared along with the pillars and... "Optimus... goodbye old friend."

Location: Unknown

Pain. Once again he was in pain. But there was something else that he felt.

 _'Cold. Why do i feel cold? Cybertronians are not really effected by temperature change on earth all that much. Which begs another question: Why is it snowing on a island in the middle of the Indian Ocean?'_ Turning his aching head he spotted his sword sticking blade down in the snow. Oddly it looked skinnier than before and the edge held no orange glow. Instead it was all silver. Rolling to his knees he reached forward but stopped noticing something very wrong. His hands were no longer silvery metal. Now they were... HUMAN! Human hands wrapped in finger-less gloves that ran to his forearms which were covered by metal bracers. A chest-plate and shoulder plates covered his grey long-sleeve shirt . He wore black leather trousers with a dark blue cloth draped around his upper legs and open in the front held by a belt, while grieves were strapped to his black boots. He also wore a helmet very similar to his original one except the face-mask did not move. The plating had a red blue and silver color scheme to it. _'What happened to me? Was it a malfunction or a glitch in the system? Could this have been the Matrix?'_

He shook his head and stood looking for a stream or pond to see the extent of the changes done to him. Sheathing his blade to his back, he wandered until he came upon a small pond that had yet to freeze over. Peering into the water he nearly choked on air. He was young by human standards, barely twenty if that. His hair was black that shone streaks of dark blue in the light. He had light stubble on his chin, also black. His eyes were the same piercing blue as before almost glowing when he looked closer. The only true blemish he had was a patch of jagged scars across his left cheek from when Megatron had nearly kicked his face in after rescuing Sam from the warehouse. Optimus shuddered at the thought. His... death... was obviously not a memory he was fond of.

Befor he could delve deeper into those morbid thoughts a heart wrenching scream tore through the forest putting Optimus on high alert. Without even pausing to think he took off toward the scream. He arrived on a boulder overlooking a road where a sled pulled by what humans called a reindeer was stopped. An injured man, with what seemes to be an arrow in his arm, the blood already soaking his shirt, and two women were aboard the sled. One woman was a red-haired girl with pigtails doing her best to treat the mans injury and wore green while the other was blonde with a braid over her shoulder in a blue dress. They were surrounded by three men. Two with swords and one with a bow. A group of bandits perhaps. ' _Where am I? Why use such primitive weapons?'_ He shook it off and stood tall.

Unsheathing his blade he called out to the attackers startling everyone below. "This is your one chance to walk away! Lay down your weapons and go home or suffer the consiquences!" _'If this comes to a fight it may be best that I don't kill them...No point in getting into too much trouble.'_ They looked at each other and shrugged. The bowman then whipped around firing an arrow but his jaw nearly fell off when the stranger simply deflected it with his blade. "Primus forgive me..." Optimus muttered before jumping clean over the sled and right on top of the closest bandit knocking him unconscious from the impact. He swiftly sliced the back of the other swordsman's leg forcing him to kneel. A hard knee-plate to the face sent him into dreamland alongside his friend. Turning to the bowman he felt a sharp sting in his left side. Looking down he sighed through his nose at the projectile protruding from between the plates of armor. Instead of wasting more time he charged. A horizontal slice destroyed his attacker's weapon followed by a pommel to the gut and an uppercut to seal the deal. Satisfied and breathing heavily he turned to the woman in blue.

"Is everyone unharmed?" She simply nodded in response her piercing blue eyes not wavering from Optimus's form. "Good... If I may-ARGGHHH!" The pain in Optimus's side nearly quadrupled and he fell to a knee then to his back. He began to black out from the pain. He barely heard the two women talking around him.

"...na I...think...the arrow...poisoned...et him...NOW!" That's all Optimus could make out as darkness took him.


	2. Chapter 2

**[A/N] Hello welcome to the second chapter of Cold Spark. I realized the original was kinda dumb... so i changed it. Anyway please leave a comment i do appreciate it. Thanks!**

 **Chapter 2: So many questions**

It's been a few months since Elsa's Coronation to Queen of Arindelle. It's winter now and in that time she has managed to get her home back on track after plunging it into Eternal Winter. Finally she manged to dig herself out of that pile of work in her study to get out of the palace, for a while at least. She took the oportunity to go for a sleigh ride with her sister Anna and Anna's beloved Kristoff. What she never could have anticipated was an arrow from seemingly nowhere slamming into Kristoff's arm followed by Anna's earsplitting scream. Now they were surrounded by bandits. Though she hated the thought of using her powers to hurt people as she did to Anna, she was more than willing to defend them but a voice above her halted everyone present.

 **"This is your one chance to walk away! Lay down your weapons and go home or suffer the consequences!"** Craning her neck she spotted a lone man in red and blue armor with sword drawn. His face covered by a helmet she had never seen before. With a twist of his blade he deflected the arrow shot from the archer then launched himself into the fray. It was over before Elsa could even react. But, unfortunately, for all his obvious skill he was still hit by the archer yet barely flinched on impact. He took down the last bandit by destroying his weapon and knocking him out. When he turned to them her eyes immediately locked to his. Just like hers they were blue but brighter, yet radiated an aura of calm and peacefulness.

"Is everyone unharmed?" She simply nodded still overwhelmed by what had just transpired. "Good... If I may-ARGGHHH!" Clutching his side he fell and Elsa finally snapped to reality and was at his side in an instant. Even with his helmet she could see he was in serious pain. Trying her best not to aggravate his wound she pulled aside the armor and shirt to see his angry red skin with dark lines spreading outwards. Her eyes widened in fear. _POISON!_

" Anna! I think the arrows they used were poisoned. We need to get him and Kristoff a doctor now!" Nodding frantically Anna went about bandaging Kristoff's wound. Elsa used her ice to stop the bleeding and hopefully slow the poison in the strangers side. The moment she did so he went completely limp. The only movement was the slow rise and fall of his chest. Knowing he was too heavy to lift even with Anna's help she created a snow golem to lift him into the sleigh . After nearly an hour they arrived at the Palace in the late hours of the afternoon and got them both situated in different rooms. Anna stayed with Kristoff while Elsa spoke to her Captain of the Guard. She explained what had transpired and sent men to round up the unconscious thugs that attacked them. They were left under the guard of the snow golem and would be easy to capture and question.

By this time the doctor returned informing her that the arrow that hit Kristoff had no poison and he would fully recover in time. "The other young man I tended to is a different story... the poison used was a weak, non lethal mixture meant to incapacitate the target. He too will heal with time but... something else caught my attention that you must see for yourself." He said adjusting his glasses on his nose. He led the queen to a spare room where he rested in bed under the warm covers. A crackling fire opposite the bed lit the room in a warm glow. His armor and sword rested nearby, the blood stained shirt she had sent to be cleaned was there as well. Getting a good look at his face she saw he was easily close to her age, perhaps older. He was also rather handsome despite his badly scarred left cheek.

"My queen. This is what I wanted you to see." The doctor said as he gently pulled the covers aside. Elsa gasped in horror at what was laid before her eyes. Slashes, stab wounds and burn scars covered his exposed upper body. The two worst ones of which were directly over his sternum and around his right shoulder. Following the queens eyes the doctor explained. "The one on his chest is the same on his back meaning he was run through with a weapon I've never seen before. The other goes all the way around his shoulder as if it were cut off yet somehow reattached. I've only ever seen the dead bear wounds such as these. The only other group that comes anywhere close are veteran soldiers returning from war. They would have to be easily twice this man's age yet he out does them all with so many. Somehow he still lives... I can't explain how."

 _'Who is this man? How has he endured these horrific wounds in such great number... Well so much for a good nights rest, now i'll be up all night thinking about this...'_ The queen thought to herself."How long until he wakes?" She asked as they exited into the hall closing the door behind him.

"A few hours at least, maybe a day... " he was interrupted by a very audible thump from the other side of the door. "Or maybe not." Entering the room again she found the bed empty and what sounded like cursing in a language she did not understand.

 **Location: Unknown**

Optimus Prime was floating in an infinite void of white. Standing in full armor he wandered, not really going anywhere until a voice boomed from everywhere at once.

 **"And so you arrive at the next step of your journey... The question is what will you become? Will you be rid of your past? Toss it away along with your strength, your resolve as well as your guilt for what you've done, and be born anew? Or will you hold that strength close and bear your burden as you have since you took your title Prime?"** The voice said.

"What do you mean? Who are you?" Optimus was so confused. ' _Born anew? What does that mean?'_

 **"I have given but a taste of what it could mean to start over. Now it is time for a final decision. You can start over, a weak human wiped clean of guilt and the sufferings of war but at the loss of your strength. Or you can once again shoulder your guilt and dark thoughts and keep your strength. Be warned... you may be as strong as a Cybertronian but if you choose this road you will never be fully human. You will be a "wolf in sheep's clothing" as it were."**

Optimus thought long and hard about this. In the end it was a truly difficult decision. But he made his choice. "I will bear the guilt as I was meant to from the start. As leader of the Autobots it was and still remains MY duty. If carrying that burden means I will be able to defend others, I shall bear it."

 **"I expected no less from you, young Prime. Always putting others above yourself... It stands as evidence of how you earned your title. Even when offered an easy way out..."** The voice said, brimming with what sounded like true adoration. **"Now you must return for only you hold the power to save them from the coming darkness. Do not worry about your name, it will be odd but with no Decepticons it won't matter. Good luck and farewell."** Then the world of vast white faded and Optimus woke to the first step of his new journey.

 **Location: Arindelle Castle**

When Optimus awoke he felt something rather odd. He was laying on something soft... which for a cybertronian is weird. He tried laying on sand once but it just got up in his wires and joints, which was extremely irritating. Opening his eyes the memories flooded back; the space bridge, the forest the fight, the woman and the strange dream. Looking around the room he found himself in a bed. He shifted the soft cover to see himself shirtless with a bandage over his abdominal and his chest littered with the scars of so many previous battles; both on Cybertron and Earth. He also spotted what appeared to be a tattoo on the inside of his right forearm, the Autobot emblem in bright red. Spying his shirt nearby he moved to get up but he accidentily rolled to far and fell out of the bed. Thankfully he fell on his right side but it didn't stop a few Cybertronian curses from escaping his lips. He failed to hear the door open but felt slender hands around his arm as someone help him to his feet. Grabbing his shirt in the process he threw it over his head rather clumsily as this was the fist time doing so.

"Are you alright?" The woman asked softly, trying to suppress a laugh at his attempts to cover himself. After a moment he managed to steady himself on his feet. Easily a head taller than her he looked down to meet her concerned, Sapphire blue gaze with a soft smile on his face; taking in her appearance of long blonde hair over her shoulder and flowing blue dress. He was blissfully unaware of how captivated she was by his eyes alone.

"I am fine. I thank you for your assistance with my wound. My name Optimus Prime. Might I ask your name and where we are?" Elsa was caught off guard, both by his near-glowing blue eyes that seemed much brighter than before as well as by his polite manner of speech. With his armor she had figured him to be a wanderer or a mercenary yet he speaks with the regality of a General. She also expected him to act like an angry berzerking barbarian based on his wounds.

"Of course. Our introductions were cut short back in the forest. I am Elsa Queen of Arendelle and it is a pleasure to meet you... Op-ti-mus?" She returned the greeting unsure as she said his strange name. He bowed his head slightly with a polite smile to reassure her. "Your name is truly unique. I've never heard of anything quite like it."

"Thank you for the compliment. As you could tell I am not from here."He chuckled a bit. _'Interesting...I've never heard of this Arendelle but it sounds similar to Arandal a city in Norway Something to look into later.'_ A small frown overtook him as his confusion deepened for a moment before he pushed those thoughts aside. Elsa was ready to ask what was wrong when a wave of pain shot from his injured side forced him to wince slightly. He had hoped she wouldn't notice but alas she did. Taking him by the arm she guided him back to the bed and sat him down. Thankfully she received no protest from him. "Thank you Queen Elsa."

"Please call me Elsa. You are a hero to my sister and I. Speaking of which I should check on her. After what happened she's more than likely still fussing over Kristoff. Oh! Dinner will be ready in an hour or so. Kai will guide to the dining room. I will see you later." Elsa said as she made for the door.

"Thank you again... Elsa." She smiled and seemed to turn a little red from what Optimus could see. He shrugged it off when something she said worried him a little. _'Oh scrap! I've never had to worry about eating human food before... Well hopefully it tastes better than Energon rations.'_


	3. Chapter 3

**[A/N] Hello everyone... It's been a while but I am back and ready for a new Chapter in Cold Spark. Dear god this took way too long to get back to. So sorry about that. Hey please leave a comment and let me know what your thinking. Thanks.**

 **Chapter 3: The Sins of the Past**

In the days following his arrival to this strange new world, Optimus Prime has had quite a few surprises of late. The first being his newfound love for food. After his first meeting with the queen and a few hours of rest, Optimus with the assistance of Kai, headed to the dining room where they were to meet for dinner. When they arrived he was sat on the queens right, across from her sister Anna who sat next to Kristoff her 'Beloved' as she said. Anna was ecstatic to finally meet their savior. Meanwhile Kristoff was welcoming yet wary of this newcomer. After they had explained what had happened with prince Hans, Optimus was more than understanding. Then came the food and Elsa nearly giggling at the sight of his wide-eyed blissful expression from the steak in front of him.

"I take it the food is to your liking?" She said struggling at maintaining her composure.

"Very much so. I've never tasted anything so unique in my life. Thank you." He said with sincerity. It was true considering the only thing he ate before this was energon which, after thousands of years... became extremely bland. With his health improved she decided to take this opportunity to learn more about the man who saved their lives.

"Optimus?" Elsa said gaining his attention. "Would you mind answering a few questions I have?"

He finished the bite of bread he was chewing and turned to her with a gentle smile. "Not at all"

She smiled back the spoke again. "Where are you from Optimus?"

Almost immediately his demeanor did a 360 turn to quiet sadness. It was like night and day with this change in atmosphere. His smile fell and his gaze dropped to the table. He spoke softly refusing to meet their gazes.

" I fear that question has no true answer. My home... is gone. And I can never return." He said solemnly as he remembered Cybertron being ripped to pieces as Sentinels space bridge collapsed on itself. At the time he felt as if his spark had been torn from him once again. Now he felt his chest sink at the sad memory. A small hand on his arm brought him back to reality.

"What Happened?" Elsa asked almost hesitantly. Finally meeting her gaze she saw nothing but pain and sadness in his eyes, who's glow seemed to have dimmed slightly. He then slowly stood and made his way to a nearby window, leaning on the ledge his meal forgotten. What he said next caught everyone off guard.

"...War... A war that ravaged our home until it was consumed by death. Our people were divided... both sides fighting for the future they believed in, the Decepticons fighting for tyranny and the Autobots who drempt of freedom and peace. Too late we discovered our home had no future... And it was all my fault. Over-matched and outnumbered our downfall was all but assured." He said looking yet not truly seeing past the glass. "Primus... I pray they can forgive me for what I've done." Mumbling the last part, he didn't think they heard.

 _'That somewhat explains the scars but... What did he mean by "My fault"... And why do you need forgiveness?'_ Elsa thought to herself as she stood up behind him. "How can one soldier be at fault for the destruction of your home? Should it not be your leaders at fault?"

"You are correct, yet you still misunderstand. It **was** our Leader who was at fault.." He then turned to her, looking her dead in the eye, his stance serious just like his voice. "Therefor the blame falls to me. We may have defeated the decepticons but it was truly a hallow victory. Now we are free... to scatter to the winds. Forgotten in the tides of time."

That's when it hit them... Elsa most particularly. She was the queen of the quiet peaceful nation who's biggest concerns were trade and tax problems. She had believed her work was tough before but now... He was their leader and now he lead nothing and no-one. She felt a tear slide down her cheek... His home his people and most likely his family... All gone. She then felt a hand on her shoulder... his hand. Warmth seemed to radiate from his touch calming her nerves and soothing her mind. The feeling was cut short as he let go.

"Do not shed your tears for me." He spoke softly then headed for the door but stopped when he reached it. "Shed them for those I failed." Resuming his course he left them standing there. When Elsa turned to her sister she found her clinging to Kristoff, her eyes watery with unspilt tears.

"Guys? What should we do?" Kristoff asked. " I know you want to help him but are you sure it's such a good idea?" Both sisters were looking at him with looks of shock and surprise at their close friend.

Anna is the first to speak. " **ARE YOU CRAZY?! HE Saved our lives and now you just want to through him out in the snow?!"**

"Think about it Anna. He just admitted to taking part in a war. That combined with how easily he took down those bandits shows that he's more than capable of killing any one of us... And I doubt he got those bad scars on his face from his parents garden." Kristoff stated plainly.

Elsa then cut in with her mind set. "While Kristoff speaks the truth... He saved our lives while risking his own. Anyone willing to give their life for another is all the proof I need to see that he has no malicious intent. I will offer him a place here If of course you approve Anna..."

Anna looked around confused for a moment then pointed to herself. "Me?" Elsa nearly rolled her eyes at her sisters antics but nodded patiently waiting for her sister to answer. "Oh... um right... important kingdom stuff... Ahem... Yes sister I believe he would be a most... benefactorial warrior to supliment our... Defensitivities..." Anna said doing her very best to look official.

Kristoff gave a hearty chuckle then kissed Anna's forhead. Elsa on the other hand gave a true heart-warming laugh at her dear sister. " I'll take that as a yes." She said followed by a quick hug before heading off with the other two heading to the stables to visit Kristoff's reindeer Sven.

As she came to the hallway with his room his room she felt eyes upon her. A sense of unease and dread surrounded her. She turned in all directions but to no avail. But this only gave time for a hooded man to drop from the ceiling at the end of the hall.

"The cold hearted witch dies here!" He said sadistically as he unsheathed two wicked daggers and started to charge her. She couldn't react in time but didn't need to when a door to the assassin's left suddenly exploded outward. Wood splinters and metal hingestore through the air followed by a blur of blue and red metal. It was then she realized it was Optimus! He barreled into his opponent sending them both through the opposite window into the gardens below. Rushing to the window she saw two forms below. The one in the dark cloak not moving while the other in full metal plating stood with little issue then kicked away the assassin's weapons before looking up. Two blue orbs glowed brightly from the tall pointed helmet in the darkening night.


End file.
